The 2005 World Health Organization Reevaluation of Human and Mammalian Toxic Equivalency Factors for Dioxins and Dioxin-Like Compounds

In June 2005, a World Health Organization (WHO)-International Programme on Chemical Safety expert meeting was held in Geneva during which the toxic equivalency factors (TEFs) for dioxin-like compounds, including some polychlorinated biphenyls (PCBs), were reevaluated. For this reevaluation process, the refined TEF database recently published by Haws et al. (2006, Toxicol. Sci. 89, 4-30) was used as a starting point. Decisions about a TEF value were made based on a combination of unweighted relative effect potency (REP) distributions from this database, expert judgment, and point estimates. Previous TEFs were assigned in increments of 0.01, 0.05, 0.1, etc., but for this reevaluation, it was decided to use half order of magnitude increments on a logarithmic scale of 0.03, 0.1, 0.3, etc. Changes were decided by the expert panel for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.3), 1,2,3,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.03), octachlorodibenzo-p-dioxin and octachlorodibenzofuran (TEFs = 0.0003), 3,4,4′,5-tetrachlorbiphenyl (PCB 81) (TEF = 0.0003), 3,3′,4,4′,5,5′-hexachlorobiphenyl (PCB 169) (TEF = 0.03), and a single TEF value (0.00003) for all relevant mono-ortho-substituted PCBs. Additivity, an important prerequisite of the TEF concept was again confirmed by results from recent in vivo mixture studies. Some experimental evidence shows that non-dioxin-like aryl hydrocarbon receptor agonists/antagonists are able to impact the overall toxic potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, and this needs to be investigated further. Certain individual and groups of compounds were identified for possible future inclusion in the TEF concept, including 3,4,4′-TCB (PCB 37), polybrominated dibenzo-p-dioxins and dibenzofurans, mixed polyhalogenated dibenzo-p-dioxins and dibenzofurans, polyhalogenated naphthalenes, and polybrominated biphenyls. Concern was expressed about direct application of the TEF/total toxic equivalency (TEQ) approach to abiotic matrices, such as soil, sediment, etc., for direct application in human risk assessment. This is problematic as the present TEF scheme and TEQ methodology are primarily intended for estimating exposure and risks via oral ingestion (e.g., by dietary intake). A number of future approaches to determine alternative or additional TEFs were also identified. These included the use of a probabilistic methodology to determine TEFs that better describe the associated levels of uncertainty and "systemic” TEFs for blood and adipose tissue and TEQ for body burde

Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife.

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties

Detection of Polychlorinated Biphenyls in the Rio Grande Basin above Cochiti Dam: Sources & Significance

Polychlorinated biphenyls (PCBs) have been detected with increasing frequency in water and fish tissue samples in the Rio Grande Basin above Cochiti Dam (RGBACD), which correlates with the use of improved analytical methods for quantifying PCBs. Levels of PCBs identified in some fish have exceeded levels considered safe for human consumption, resulting in a Fish Consumption Advisory\u27 for Abiquiu and Cochiti Reservoirs and the Rio Grande from Pojoaque Creek to Frijoles Canyon (Bandelier National Monument). In June of 2007, the New Mexico Environment Department (NMED) listed seven water bodies in the RGBACD as impaired due to elevated concentrations of PCBs in fish tissue and water samples collected from the area. These actions, a review of PCB related research conducted within the RGBACD, and a comparison between Aroclor and congener analytical results initiated research investigating the following issues: 1) whether PCBs are more prevalent in water, sediment, and fish tissue samples now than determined in field studies prior to 1997, 2) where the most likely sources of PCB contamination in the RGBACD are located, 3) whether canyons on LANL property are contributing to PCBs in water and sediment within the Rio Grande and in fish at Cochiti Reservoir, 4) if sediment contamination poses a potential risk, and 5) the appropriate fish consumption limits for fish caught in Cochiti and Abiquiu Reservoirs. This paper describes a study that generated information related to the occurrence, distribution, and potential sources of PCBs in the RGBACD. Results from samples collected upstream and downstream of Los Alamos National Laboratory contradict previous research concluding it was not a major source of PCBs in fish tissue at Cochiti Reservoir. Concentrations in carp, catfish, rainbow trout, and walleye collected in 2006 by the NMED Surface Water Quality Bureau fall within the recommended monthly EPA fish consumption limit category. Preliminary recommendations to better characterize PCBs in the RGBACD are offered as a result of the study

A Compilation of Europe-Wide Databases from Published Measurements of PCBs, Dioxins and Furans

Chemical risk assessment always entails an evaluation of expected environmental concentrations of substances; these concentrations may be predicted using mathematical models or may be chosen on the basis of experimental observations and monitoring activities. The work discusses the usefulness and limitations in building compilations of published monitoring data by describing a feasibility study on polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), for which observed concentration data were retrieved from scientific journal articles published between 2000 and 2009. These chemicals are typical POPs and are of constantly high concern for their potential adverse effects on human health and ecosystems. PCBs were mainly used by the power industry in electrical transformers, capacitors, hydraulic equipment, and as lubricants. PCDD/Fs are formed as unintentional by-products of chemical manufacturing and incineration processes, as well as natural processes such as volcanic eruptions, and biomass burning. Emissions from incineration of industrial wastes such as metal reclamation and domestic heating (especially in central Europe) are considered as current sources of PCDD/Fs to the environment. A database of published observed concentrations of PCBs and PCDD/Fs in air, soil sediments and water was built as described in details in the report. As continental scale assessment is aimed more at the evaluation of the regional distribution of contamination, we excluded from the database those measurements taken close to known PCB or PCCD/F pollution sources of exceptional entity such as waste incinerators or contaminated sites. After presenting and interpreting the results of the literature search, we critically examine the completeness and usability of this information, and the usefulness of data compilations in the framework of chemical risk assessment.JRC.H.5-Rural, water and ecosystem resource

Congener patterns of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls as a useful aid to source identification during a contamination incident in the food chain

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) are still considered among the most important groups of contaminants in the food chain. Self-control by food producers and official control by authorities are important activities that allow contaminant sources to be traced and promote further reduction in food and feed levels. Strict but feasible maximum levels were set by the EU Commission for food and feed to support this strategy, as well as action levels and thresholds. When products exceed these levels, it is important to trace the source of contamination and take measures to remove it. Congener patterns of PCDD/Fs and PCBs differ between sources and are important tools for source identification. Therefore, patterns associated with different sources and incidents relating to various feed matrices and certain agricultural chemicals were collated from published scientific papers, with additional ones available from some laboratories. The collection was evaluated for completeness by presentations at workshops and conferences. Primary sources appear to derive from 5 categories, i) by-products from production of organochlorine chemicals (e.g. PCBs, chlorophenols, chlorinated pesticides, polyvinyl chloride (PVC)), ii) the result of combustion of certain materials and accidental fires, iii) the use of inorganic chlorine, iv) recycling/production of certain minerals, and v) certain naturally occurring clays (ball clay, kaolinite). A decision tree was developed to assist in the identification of the source

Toxicological profile for chlorodibenzofurans (CDFs)

VERSION HISTORYDate DescriptionApril 2023 Final toxicological profile releasedJanuary 2022 Draft for public comment toxicological profile releasedMay 1994 Final toxicological profile releasedtp32.pd

Toxicological profile for chlorodibenzofurans (CDFs) : draft for public comment

VERSION HISTORYDate VersionJanuary 2022 Draft for public comment releasedMay 1994 Final toxicological profile releasedtp32.pdf20221104